This past spring, however, the tremendous amount of ice in the Ross Sea forced the penguins to walk rather than swim to their colonies.

Penguins at the Cape Royds colony, for instance, had to walk an additional 80 miles (129 kilometers), said researcher David Ainley. He is in Antarctica conducting long-term studies of Adélie penguins under a grant from the National Science Foundation, in collaboration with researchers from Landcare Research New Zealand.

Penguins can swim much faster than they can walk. They generally swim from four to five miles (seven to eight kilometers) per hour; their walking speed is roughly four times slower than that. This means that what would normally be an 18-hour trip took about 90 hours this year.

And that's not round trip.

Watching the Ice

There are two kinds of sea ice in Antarctica: fast ice and pack ice. Both kinds have caused problems for the penguins this year, researchers say.

"The fast ice, which is a solid continuous plate of ice connected to land, was more extensive than ever recorded," said Gerald Kooyman, a biologist at Scripps Institution of Oceanography in La Jolla, California, who was in Antarctica in December studying Emperor penguins.

In October, fast ice extended roughly 80 miles (129 kilometers) into the Ross Sea. The norm is 15 to 20 miles (24 to 32 kilometers).

"The only bird or mammal that can use fast ice as habitat is the Weddell seal," Kooyman noted.

Pack ice is sea ice that has broken into floes. "The pack ice in the Western Ross Sea didn't seem unusual in amount, but in the eastern Ross Sea there was a lot of ice," said Kooyman.